[Coco] [Spam] hardware scrolling

[Simon Jonassen]

Hey Nick !

The scroll routine can already scroll any section of the screen i choose...

I just made it scroll the whole screen for the effect....

The scroll routine does sync on horizontal scanlines and changes mode from a
16 byte to a 32 byte mode, but with them sam set to 42 byte DMA mode which
provides you with horizontal scrolling... 

By varying the line you "split" the screen on it pushes the bitmap
left/right... The 42 byte mode provides you with extra "room" on each side
of the bitmap so you can introduce more graphics.....

The scroll routine is essentially messing with the vdg/sam address
counters...

/Simon :-)
 

-----Oprindelig meddelelse-----
Fra: coco-bounces at maltedmedia.com [mailto:coco-bounces at maltedmedia.com] På
vegne af Nick Marentes
Sendt: 26. oktober 2013 07:53
Til: CoCoList
Emne: [Spam] [Coco] hardware scrolling

This is not a new feature. It's been known. I just don't think that anyone
used it.

Does anyone know of a CoCo 1/2 game that actually used the ability to set
start of video for vertical or horizontal scrolling? I think everyone just
used software which allowed for 1 byte movement. As it stands, it jumps in
increments of several bytes (6?).

Also, same problem as the CoCo3 GIME... it moves the whole screen.

Simon, your next challenge is split screen scrolling which I think the VDG
would be able to do by syncing on the horizontal scanlines and changing the
$FF22 at set points.

Nick

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